Standard photovoltaic installations comprise in general a centralized converter which has typically only one input channel able to perform individual Maximum Power Point Tracking (MPPT).
Photovoltaic modules are made of several strings of cells (for example 3 strings in a panel). A string of cells is the serial connection of several photovoltaic cells (for example 32 cells per string in one panel). These strings of cells are serial connected in the photovoltaic junction-box.
To each of these strings a by-pass diode can be associated in the photovoltaic junction box. These by-pass diodes arm to prevent damaging of photovoltaic cells when partial shadowing occurs (hot-spot). The photovoltaic modules are then serial connected to rise-up the voltage and match the nominal voltage of the central converter.
Several strings of modules can finally be parallel connected to match the nominal power of the central converter.
In this configuration, shading by chimneys, trees, power lines, soiling from dust, debris, and bird droppings, (and also panels' mismatch due to manufacturing tolerance, ageing, etc.) can cause significant power losses in both shaded and non-shaded modules.
Even more, it is commonly reported that, on average, residential and commercial installations are 25% smaller than they could be, because they are designed around shadowing problems and irregular roof shapes.
A solution to this problem might be to use a distributed photovoltaic system architecture. The concept of a distributed photovoltaic system has become possible with the deployment of micro-converters or micro-inverters able to perform MPPT at a photovoltaic module scale (or even a string of photovoltaic modules scale).
However, this association of multiple micro-converters, or micro-inverters, can only solve a part of the problems related to partial shadowing and different tilt or orientation angles of photovoltaic modules.
In addition, the increasing number of micro-converter results in a cost increase of such photovoltaic panels.
U.S. Pat. No. 6,350,944 relates to a solar module with reconfigurable tile.
This document describes a reconfigurable solar cell panel having a system of integrated solar-power generation cells with monitoring control and reconfiguration circuitry in a modular array scheme. A plurality of solar cells is packaged on a printed circuit board to form a solar module, also known as a solar module array configurable tile (SMART) module. A solar panel is made up of a plurality of modules that are electrically connected together. The printed circuit board is the physical support structure for the array of solar cells and provides the electrical connection paths between the solar cells comprising the solar cell module. Each solar cell on the module is part of a matrix of solar cells. A plurality of modules is assembled into a solar panel.
However, the solution in this document is cumbersome and expensive as routing as well as switching takes place between the solar cells on the substrate. In addition, not only routing lines for energy flow, but also control lines for controlling the transistors have to be foreseen which will render solar panels more expensive. This document is silent to connection of the solar panel to a converter.
WO2008076301 discloses a photovoltaic module utilizing a flex circuit for reconfiguration.
Even if this document discloses that photovoltaic cells may be connected in series, in parallel or isolated upon the environmental conditions, only one converter is used. Thus reconfiguration and therefore converter capacities are not used in an optimized manner.
WO2009060273 relates to a method of operating and device for controlling an energy installation comprising photovoltaic modules and inverters in which a selection and control unit selects combinations of connections of the photovoltaic modules and controls a switching unit as to establish a selected combination.
Although this document discloses to realize a serial/parallel connection in order to supply to the input of the converters current in their working range, the solution in this document does not allow taking into account efficiently the whole chain from the PV cell to the output of the converters.
The present invention aims at mitigating, at least partially, the drawbacks described above, in particular for enhancing power conversion.
For this purpose, the invention proposes an electronic management system for electricity generating cells, the system comprising:                cell connection terminals to be connected to n associated electricity generating cells, n being a positive integer number,        outputs to be connected to m associated static converters; m being a positive integer number and at least m=2,        an energy routing module adapted for routing energy flows from and between said cell connection terminals towards said outputs; and        an electronic control unit adapted for controlling dynamically the energy routing module.        
Thanks to the dynamical energy routing to the converters, power conversion can be optimized. The electronic management system is versatile to adapt to many different situations. The electronic management system does not interfere with the construction of the electricity generating cells and can be integrated in a simple way in an electricity generating system.
In a particular embodiment, the electronic control unit comprises:                first sensors within the group comprising voltage and/or current sensors at a cell connection terminal,        second sensors comprising a voltage and/or current sensors at outputs of the static converters,        
and the electronic control unit is arranged to reconfigure dynamically the switches of said energy routing module in function of the output of said first and second sensors.
Thus, in taking into account sensor measurements at cell connection terminals on the one side and the output of the static converters on the other side, the overall chain (cell, energy routing module, converters) can be taken into account. The invention therefore allows optimizing at least one parameter in the group of (i) instant power at the output of the converters or (ii) aging of the converters.
If the parameter is the instant output power of the converters, then optimizing would mean to maximize the instant power output of the converters.
If the parameter is aging of the converters, the optimizing would mean to operate the converters in an operation state that reduces the aging effect, for example by functioning at lower temperature that induces less stress.
As another example, if the output power at cell level has been optimized for the entry of for example one selected converter to figure in his operating range, it might be that during operation, the temperature of the converter rises and the converting efficiency decreases. In this case, the control unit would observe through the detectors at the output of the converter the decrease in power while the power at the cell connection terminals is still the same. The control unit is then programmed to deduce that in that case, the switches of the energy routing module shall be reconfigured dynamically in order to set in service another converter or a second converter in parallel to the first one. The instant power output of the system would re-increase and overall power output is optimized.
According to other characteristics taken alone or in combination:
According to one aspect, m being a positive integer less than n.
This contributes for minimizing the number of used converters and reducing the overall cost of the electricity in particular compared to a fully distributed power conversion system.
According to another aspect, the system comprises at least 2n cell connection terminals and at least 2m outputs.
According to one aspect, the energy routing module comprises an electrical connection map between said cell connection terminals and said outputs and switches disposed in the electrical connection map for routing the energy from and between at least one of said cell connection terminals to at least one of said outputs.
The electrical connection map and the switches may be configured to provide at said outputs several serial and/or parallel connections of said cell connection terminals.
According to one aspect, the switches have low ohmic resistance in conduction state.
Said switches may be electromechanical switches, MOSFET transistors or IGBT switches.
The electronic control unit may be arranged to reconfigure dynamically the switches of said energy routing module upon a change in a control parameter, which control parameter may be at least one parameter of the group of parameters comprising: environmental temperature, irradiance of at least one photovoltaic cell, a converter duty cycle of at least care converter, a failure flag, produced power level.
According to another example, the electronic control unit is arranged to reconfigure dynamically the switches of said energy routing module on a periodically basis.
According to a further example, the electronic control unit may be arranged to reconfigure dynamically the switches of said energy routing module upon an estimated optimal power output based on past energy routing configurations.
Furthermore, the electronic control unit may be arranged to reconfigure the switches of said energy routing dynamically module upon the optimisation of a power cost function.
The electronic control unit may be configured to alternate period of operation of said outputs.
According to another embodiment the energy routing module comprises furthermore at least p supplementary outputs, p being a positive integer number and p≧1, connected to correspondent p supplementary input terminals of said energy routing module forming a loop connection between said p outputs and said p input terminals.
At least one of said loop connections may comprise a static converter.
The invention concerns also an electricity generating system comprising:                at least n electricity generating cells, n being a positive integer number,        at least m static converters; m being a positive integer number and at least m=2, and        an electronic management system as described above, the electronic management system comprising:        cell connection terminals connected to n associated electricity generating cells,        outputs connected to m associated static converters;        an energy routing module adapted for routing energy flows from and between said cell connection terminals towards said outputs; and        an electronic control unit adapted for controlling dynamically the energy routing module.        
In a particular embodiment, the electronic control unit comprises:                first sensors within the group comprising voltage and/or current sensors at a cell connection terminal,        second sensors comprising a voltage and/or current sensors at outputs of the static converters,        
and the electronic control unit is arranged to reconfigure dynamically the switches of said energy routing module in function of the output of said first and second sensors.
In some embodiments m may be less than n.
The electricity generating cells may be photovoltaic cells, photovoltaic strings comprising several photovoltaic cells, or electrochemical cells or fuel cells.
According to one aspect, said converters comprise an MPPT control unit.
Said m static converters may be divided in at least two groups of converters exhibiting different power ranges and/or conversion technology.
The invention also concerns a method for electronically managing energy flow between at least n electricity generating cells, n being a positive integer number, and at least m static converters; m being a positive integer number and at least m=2, comprising the step of dynamically routing energy flows from and between cell connection terminals connected to the electricity generating cells towards said outputs.
In a particular embodiment, the method further comprises the steps of:                detecting eel values comprising voltage and/or current values of the cell connection terminals,        detecting converter values comprising voltage and/or current values of outputs of the static converters,        dynamically routing energy flows from and between cell connection terminals connected to the electricity generating cells towards said outputs, at least some outputs being connected to said at least m static converters in function of the cell values and of the converter values.        
According to one aspect m may be less than n.
According to one aspect the method comprises the following steps:                detection of operation state of converters between working converters and non-working converters because of a failure;        dynamically routing energy flows from and between 2n cell connection terminals connected to the electricity generating cells towards said working converters.        
In an embodiment, the detection of operating state of converters is based on a detection of converter values comprising voltage and/or current values of outputs of the static converters.
According to another aspect where said electricity generating cells are photovoltaic cells, the method may comprise the following steps:                detection of irradiance state of PV cells between at least two classes of irradiance states in particular shaded PV cells and non-shaded PV-cells;        dynamically routing energy flows from and between cell connection terminals connected to the electricity generating cells towards said converters in connecting only PV cells of same class of irradiance state in series to a converter.        
According to another aspect the period of operation of said outputs is alternated in a rotating manner to equalize the operation time and/or the energy processed by each converter.